The heart of a computer's long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider toward the surface of the disk, and when the disk rotates air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head can include a magnetic write pole and a magnetic return pole, the write pole having a much smaller cross section at the ABS than the return pole. The magnetic write pole and return pole are magnetically connected with one another at a region removed from the ABS. An electrically conductive write coil induces a magnetic flux through the write coil. This results in a magnetic write field being emitted toward the adjacent magnetic medium, the write field being substantially perpendicular to the surface of the medium (although it can be canted somewhat, such as by a trailing shield located near the write pole). The magnetic write field locally magnetizes the medium and then travels through the medium and returns to the write head at the location of the return pole where it is sufficiently spread out and weak that it does not erase previously recorded bits of data.
At very small bit sizes it is very important to define the write pole very accurately. As one of the most important processes in magnetic head write fabrication, the hard mask formation and its performance control play critical roles for the subsequent manufacture processes to achieve high production yields. One example is the formation of a Si containing dielectric hard mask which is used as hard mask for the subsequent underlayer mask reactive ion etching (RIE). The dielectric hard mask pattern is formed by transferring a photoresist mask pattern onto a dielectric hard mask layer using a fluorocarbon containing chemistry RIE process which is different from underlayer mask RIE, where an oxygen containing chemistry is used.
Usually, the dielectric hard mask layer is much thinner than the under-layer mask. This is acceptable because of the high selectivity of the dielectric hard mask to underlayer in oxygen RIE. However, processes used to manufacture the write pole by defining a mask structure typically result in the underlayer mask structure being poorly defined, with rough sidewalls, irregular undercuts and other deformities. This makes an accurate definition of the write pole difficult to achieve.